The invention relates generally to and is an improvement of reinforced tubular metal bats such as the Easton Aluminum, Inc. ("Easton") "C-Core" product disclosed in U.S. Pat. No. 5,364,095, which is hereby incorporated by reference as if it were set forth herein in its entirety. Baseball and softball bats today are typically made from aluminum or an aluminum alloy and are generally hollow inside. Such bats generally have a tubular outer shell comprising a barrel portion, a tapered portion, and a handle portion; a knob covering the end near the handle portion; and a cap covering the far end. Improvements in today's baseball and softball bats are directed to providing a wider "sweet spot," to reducing the sting and discomfort that often results from hitting the ball other than on the sweet spot, and to providing these improvements at reasonable costs and without sacrificing the bat's durability.
Bats have been improved by crafting the tubular outer shell entirely from titanium. This, however, raises the costs prohibitively because the titanium is very expensive and difficult to form. A titanium bat would have a retail sale price between 400 and 700 dollars.
Over the years, there have been many attempts to approach and surpass the level of performance rendered by the titanium bat without the commensurate costs. Most bat improvements today focus on the use of inserts that reinforce the barrel portion of the tubular outer shell. The object of using reinforcing inserts is to increase the compliance (flexibility) of the bat while simultaneously controlling the stress in the outer shell. That is, the reinforced bat is more compliant (or flexible) and can deflect more before experiencing permanent set or yield (that is, before it is dented). A more compliant bat is said to enhance player comfort and performance by reducing the amount of sting that can be experienced during ball impact. A more compliant bat is also said to have a wider "sweet spot." The use of reinforcing inserts also allows the manufacturer to make the barrel portion of the outer tubular shell substantially thinner, which may tend to make the bat lighter and/or reduce its material costs. Use of an appropriate reinforcing member in conjunction with a barrel with a thinner outer tubular shell provides a more compliant bat because such a design allows the outer shell to freely flex while offering enough modulus of elasticity (stiffness) to prevent the shell from deflecting to yield (denting).
One such approach is disclosed in the Easton U.S. Pat. No. 5,364,095, which discloses a bat with a reinforced fiber or composite material insert in compressive engagement with the barrel's outer shell. Others have attempted to increase bat compliance in several ways.
U.S. Pat. No. 5,414,398 to Eggiman, which is hereby incorporated by reference as if it were set forth herein in its entirety, discloses a bat with a tubular insert. The outside diameter of the insert is smaller than the inside diameter of the bat's outer shell so that there exists an annular gap between the two. The outside shell and tubular insert are therefore able to act independently and, by so doing, together act as a leaf spring, which is said to increase bat compliance while moderately limiting the force required to yield (dent) the barrel portion.
U.S. Pat. No. 5,676,610 to Bhatt et al., which is hereby incorporated by reference as if it were set forth herein in its entirety, teaches inserting a sheet of metal, wound into a spiral spring, into the bat's barrel. The sheet is of sufficient length to wrap 1.1 to 3 times the inside circumference of the tubular bat barrel.
U.S. Pat. No. 5,511,777 to McNeely, which is hereby incorporated by reference as if it were set forth herein in its entirety, teaches a bat having a rebounding core therein. The McNeely bat comprises a resilient attenuator sleeve compressed between the bat's outer shell and an inner damper, fashioned from brass or a similar material. The resilient attenuator sleeve may be fashioned from a polystyrene closed cell foam.
Despite the advances claimed in these patents, today's most expensive and supposedly "high performance" bats are still susceptible to denting. Alternatively, the more durable bats are not sufficiently compliant.